The present invention relates to a device for the non-destructive testing of an upright cylindrical nuclear reactor pressure vessel in which a likewise cylindrical coaxial nuclear fuel container is disposed. The device includes a vertical mast projecting into the pressure vessel and mounted so as to be displaceable at its upper and lower ends in the circumferential direction of the pressure vessel. The mast is equipped with a carrier for test instruments which can be displaced along the mast. Devices of this type are disclosed, for example, in German Offenlegungsschrift [laid open patent application] No. 2,644,261 and corresponding U.S. Pat. No. 4,081,325.
The pressure vessels of nuclear reactors are known to be composed of several bent, plate-shaped or preferably annular components, with the components being interconnected by weld seams. The weld seams and the parts of the plates immediately adjacent the seams constitute critical regions in the pressure vessel since, due to inclusions, blowholes or bubbles, brittlenesses and other faults, they may include zones of lower strength. For this reason it is absolutely necessary to test the entire pressure vessel, and particularly the above-mentioned zones, for freedom from faults before it is put into operation for the first time and also during its operation. This is generally done with the aid of ultrasonic devices which detect and localize inclusions and blowholes due to their echo behavior which differs from the remainder of the material. To perform such tests, it is necessary to guide the test instrument with great accuracy along the interior or exterior wall of the pressure vessel and to provide means which continuously, and with great precision, record the position of the test instrument. The technical difficulties arising in this connection become evident if one realizes that the height of such a pressure vessel may be 10 meters and more. The manipulator which guides the testing devices and brings them to their locations of use, must be able to indicate the respective position of the test instrument with an accuracy of .+-.3 mm.
The aforementioned mentioned German Offenlegungsschrift No. 2,644,261 and corresponding U.S. Pat. No. 4,081,325 disclose a test manipulator which is essentially composed of a vertically arranged mast that is mounted so as to be movable on running rails disposed at its upper and lower end. The running rails are angularly arranged around the cylindrical nuclear fuel container so that the mast can be displaced circumferentially with good guidance from the top and bottom. A vertically displaceable carrier for the test instruments is mounted at the mast. The entire device is disposed in the gap between the nuclear fuel container and the inner wall of the pressure vessel and is of relatively simple construction.
Test manipulators of this type can be used only if reactor constructions are involved in which the annular space between the nuclear fuel container and the inner wall of the pressure vessel does not include any interfering, built-in structures, such as conduits or other fittings. This is frequently the case in more modern reactor designs. However, numerous older designs exist which do not meet this requirement so that manipulators of this type cannot be used in such cases.